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Gene Expression
Gene Regulation
Regulatory Gene
Antisense Strand
Initiation Site
3’
R
O
P
-35
ORF
1st nt
Genes
-10
Operator Gene
Translation
Repressor protein
Regulation Operons
5’
Gene Regulation
Genes Encode Functions NOT Always Required
E. coli in Glucose Medium containing Amino
Acids
No Need for Enzymes to Alternate C
Lactose
No Need to Synthesis Amino Acids
Regulation Needs
Nutritional Environment
Physical Environment
Signals that facility Transcription ‘+”
Signals that interfere with Transcription “-”
Regulation Occurs at Any Level
Transcription* - Binding RNA Polymerase at P site
mRNA - amount of Turn over Alter Sigma’s
“Strength of P”
Translation Step
Enzyme Function- Repressor or Reduction
General Features of Regulation
Constitutive: Expressed All Time
Gene Switch always on
Enzymes and Structural
Adaptive or Inducible
Only if Needed
Regulation
Specific
Controlling one gene or Operon
Global
Controlling Wide Range
Nutritional or Physical
Anaerobic Respiration
Heat Shock
Osmotic Stress
Major Modes of Regulation
Activity of Preexisting Enzymes:
Posttranslational
Course Control
Rapid-Seconds
Amount of Enzymes:
Transcription
Slow in terms of Minutes
New Enzyme Synthesis
Dilution of Existing Enzymes
Inhibiting Enzyme Activity
Posttranslational
Some Enzymes Need Processing for Activity
Most Enzymes Synthesized With Full Activity
Therefore Need specific Cell Inhibitors
Feed Back Inhibition
Final Product of Biosynthetic Pathways Block
The 1st Enzyme in the Reaction
Assimilation of ammonia
Modification of
Enzymes
Glutamine Synthetase
Glutamine Synthetase
HOW? Feed back Works
Allostery
Active Site: substrate Binds
Allosteric Site: the Inhibitor or “ Effector” Binds
Isoenzymes
Regulation of Transcription
Control of Amount of Protein
Switch “ON” All Time unless “Off” repressor Protein
P Site on Operon Very Close to Consensus
Consequence
Shine-Dalgarno Complimentary to 16S rRNA
More gene Transcribed More the Amount
Regulatory Gene
Antisense Strand
Initiation Site
3’
R
O
P
-35
ORF
1st nt
Genes
-10
Operator Gene
Translation
Repressor protein
Regulation Operons
5’
Negative Control of Transcription
Switch is always on: Needs a repressor protein
to cut off
Two ways to happen:
Enzyme Repression ; Ex. AA Arginine is
Synthesized if: NO Arginine present in medium
Enzyme Reduction: The Synthesis of an Enzyme
ONLY if Substrate is present
Terms
Bacteria Adapt to Specific Conditions By altering levels
of mRNA
Constitutively- is without Control only Strength of Promoter
Adaptive – Ability to initiate Transcription –Control by signal Proteins
Environmental Signals facilitate Transcription
Positive Regulation
Environmental Signals interfere with Transcription
Negative Regulation
Negative Regulation
Terms:
Inducer: Substance Initiates Enzyme Induction
Co repressor: Represses Production
Collectively Called Effectors (small molecules)
Negative Regulation
Enzyme Reduction
LAC Operon:
No Lactose Present-Repressor binds to
Operator Near Promoter- NO Transcription
Lactose Present: Repressor & Inducers
(allolactose) bind to Prevent binding repressor
Positive Regulation
Signaling Proteins
Activator Proteins Not Repressor
Together Stimulate Transcription
Tryptophan
Maltose
Catabolite Activation
Lactose present
Low Glucose (Note: Glucose Inhibits CAMP)
cAMP
Complex with Catabolite Activator Protein CAP
Together they bind to polymerase to Activate
Transcription
Diauxic growth
b-galactosidase
Catabolite Activator
Protein CAP
cAMP
B-galactosidase
TWO COMPONENT Regular System
Sensor Kinase: Phosphorylases its’ self in response
to environmental Signal
Response Regulator: Acts as Repressor
Osmoregulation of gene expression